In work on monoclonal antibodies, as well as in other endeavors, it is desirable to be able to isolate individual cells. We are developing an inexpensive device for placing one, and only one cell in each well of a microtitre tray, in culture medium. Thus, the progeny in each well will all be descendents of that single cell, or monoclonal. Our device is an improvement over the existing technique of limiting serial dilution, because each well contains a single cell, while a tray filled by the limiting serial dilution technique will contain many empty wells, and may also contain a few wells that contain two or three cells. The device will be fully automated, requiring minimal operator intervention.